1 / 19

PHYS16 – Lecture 7

PHYS16 – Lecture 7. Ch. 5 Force and Newton’s Laws. http://fashionablygeek.com/wp-content/uploads/2009/09/mass-times-acceleration.gif. Motion - Review. Constant, non-zero acceleration in y leads to displacement in y that is A) linear B) parabolic C) constant D) exponential

owena
Download Presentation

PHYS16 – Lecture 7

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. PHYS16 – Lecture 7 Ch. 5 Force and Newton’s Laws http://fashionablygeek.com/wp-content/uploads/2009/09/mass-times-acceleration.gif

  2. Motion - Review • Constant, non-zero acceleration in y leads to displacement in y that is A) linear B) parabolic C) constant D) exponential E) None of the above

  3. Motion - Review • A ball accelerates from rest at 10 m/s2 at an angle of 30 degrees with respect to the ground for 2 s. What is the ball’s final velocity? A) 19 m/s at -30 degrees B) 20 m/s at -30 degrees C) 20 m/s at 30 degrees D) 20 m/s at 0 degrees E) None of the above

  4. Motion - Review • A projectile is fired at a 30 degree angle. Which of the following statements is true. • When the projectile reaches its maximum height the velocity is zero. • When the projectile reaches its maximum height the acceleration is zero. • The acceleration of the projectile just after it is fired is the same as just before it lands. • The velocity of the projectile just after it is fired is the same as just before it lands • None of the above.

  5. Motion – Review • A police car, traveling at 95 km/h, is trying to catch a motorist at 80 km/h. Is the police car’s speed relative to the motorist the same as the motorist’s speed relative to the police car? • Yes • No • Not enough information

  6. Ch. 5 Force • Force – Definition & Types • Newton’s Laws • Law of inertia • F=ma • Faction= -Freaction • Friction • Applications of Newton’s Laws

  7. Force pre-question • A locomotive breaks through a wall at a train station. Which of the following is true? A) (force exerted by locomotive on wall) > (force exerted by wall on locomotive) B) (force exerted by locomotive on wall) is equal and opposite (force exerted by wall on locomotive) C) (force exerted by locomotive on wall) < (force exerted by wall on locomotive) D) the wall does not exert a force; it broke

  8. Force: Definition & Types

  9. Force - Definition • A push or a pull that can change an object’s motion Contact Forces – need to contact object Tension – reaction force along rope away from object Compression – a push Normal – reaction force that is perpendicular to surface Friction – breaking of bonds along surface that resist motion Biological – forces applied by people Fundamental Forces – Long range Gravity – attraction btw masses Electromagnetic – attraction/repulsion btw charges Strong – holds protons & neutrons in nucleus Weak – responsible for neutrino/beta decay

  10. Forces act at: • Contact forces act at the point of contact • If we can assume the object is a point object then we can draw these forces acting at the center of mass • Long range forces act at the center of mass

  11. Center of Mass • Center of mass is geometric center of object weighted by the object’s mass distribution • Assume density is the same throughout following objects and find center of mass:

  12. Most Common Forces • Gravity • Normal • Tension • Friction

  13. Newton’s Laws

  14. Newton’s Laws – First Law • A body at rest remains at rest & a body in motion stays in motion unless acted on by a force • Doesn’t seem true because most objects don’t infinitely stay in motion, why? (friction) • Can see this is true if decrease air friction • Example – Brick pushed along ground vs. Brick in cart pushed along ground

  15. Newton’s Laws – Second Law • If there is a NET force then the object is accelerated in the direction of the force. • The magnitude of the acceleration is proportional to the force and inversely proportional to the object’s mass.

  16. What happens if there is no net force? • Scenario #1 – there are forces acting on the object, but they cancel • Scenario #2 – there are no forces acting on the object • If there is no NET force then no acceleration

  17. Mechanical Equilibrium • Mechanical Equilibrium – when FNET=0 • Static Equilibrium • v= 0 • FNET=0 • Example – book on a table • Dynamic Equilibrium • v= constant • FNET=0 • Example – car moving at constant speed

  18. Newton’s Laws – Third Law • Every action has an equal and opposite reaction • Does this seem true? If I push a block does it push back on me? • Yes, I just have friction from floor keeping me in place • Can feel pressure of block on fingers • So all reactionary forces – Normal, Friction, Tension will vary with the amount of applied force

  19. Conclusions • Force • Push or pull • Vector quantity • Newton’s laws • Law of inertia • F=ma • Faction = -Freaction

More Related